Port the remaining of dart:core to the unified corelib.

corelib/unified/core/expando.dart

Index: corelib/unified/core/expando.dart
diff --git a/corelib/src/expando.dart b/corelib/unified/core/expando.dart
similarity index 95%
copy from corelib/src/expando.dart
copy to corelib/unified/core/expando.dart
index e21c5aaf071ba072d11417527eb83c37c9b4dbdf..d537659146000ba03d5c339cd2f40adb432fb19b 100644
--- a/corelib/src/expando.dart
+++ b/corelib/unified/core/expando.dart
@@ -5,7 +5,7 @@
 /**
  * An [Expando] allows adding new properties to objects.
  */
-interface Expando<T> default _Expando<T> {
+interface Expando<T> default ExpandoImplementation<T> {

[Mads Ager (google), 2012/08/01 14:33:08]

Have you made ExpandoImplementation public because that is what is usually done
for the rest? I'm not sure that it makes much sense to have
ExpandoImplementation be public?

[Anders Johnsen, 2012/08/01 14:39:08]

I did it to get around a privacy issue. dart:core imports coreimpl, but that
also means that if I put _Expando in coreimpl, it'll not be accessible from
here. Should we put the implementation in this file as _Expando?

(Note that the old version _sources_ it in from mock.dart)

[Mads Ager (google), 2012/08/01 14:42:37]

I think this is fine. But maybe you can follow up offline with the author of
Expando to clearify its usage and why it was implemented this way?

[Anders Johnsen, 2012/08/02 10:17:41]

Will do!

 
   /**
    * The name of the this [Expando] as passed to the constructor. If